Pryor’s re-election race is 17 months away, but the Democratic incumbent seen as perhaps the most vulnerable in 2014 is already taking hits from the right and the left. That’s forced the second-term senator to aggressively defend himself and step into re-election mode sooner than planned, even though he has no Republican opponent.

“My goal right now is to put the campaign off until the election year, 2014,” Pryor told reporters recently. “They keep dragging me back into the politics, they keep running ads and trying to keep it stirred it up here.”

Republicans are trying to unseat Pryor and three other Democratic incumbents who represent states that Republican Mitt Romney won in last year’s presidential race: Mark Begich of Alaska, Kay Hagan of North Carolina and Mary Landrieu of Louisiana.

Democrats need to defend 21 seats, including seven in largely rural states that Obama lost in 2012.

Republicans need to pick up six seats to regain Senate control. But the GOP is defending fewer incumbents and could benefit from history: The party controlling the White House usually loses seats during the midterm election of a second-term president.

Pryor, who began airing his first television ad last month, faces pressure especially early in Arkansas. He’s trying to survive in a state where Republicans enjoyed widespread gains over the past two election cycles, fueled by Obama’s unpopularity.

The GOP controls both chambers of the Legislature and all four U.S. House seats. In 2010, Democratic Sen. Blanche Lincoln lost her bid for a third term. Last year, Republicans swept all four House seats and won control of the Legislature for the first time since Reconstruction.

National and state Republicans are eager to topple Pryor, whose father, David, was a senator and governor. It’s a turnaround from 2008, when Republicans were unable to find anyone to challenge Mark Pryor and he easily won a second term.

“When you hear Arkansas Democrats try to spin things for Mark Pryor, the only things they can point to is he’s raised a lot of money, he’s got a high name ID and the fact his father is popular,” David Ray, a spokesman for the state GOP. “That’s not a very strong place to start.”

Among Republicans, U.S. Reps. Tom Cotton and Steve Womack are widely viewed as potential challengers.

So far, Pryor is taking heat from outside groups rather than a challenger. The Senate Conservatives Fund, a political action committee, has begun airing $320,000 worth of television ads criticizing Pryor’s 2009 vote for the federal health care law and calling him too liberal.

The conservative Club for Growth, which backed Cotton last year, has aired ads linking Pryor to Obama.

At the same time, Pryor has absorbed criticism from the left after voting against expanded background checks for firearms purchases.

Mayors Against Illegal Guns, the Bloomberg group, is airing television and radio ads criticizing Pryor for the vote. The ad invokes the shooting death of Bill Gwatney, the state Democratic Party chairman who was killed in his office in 2008. Bloomberg has also urged New York donors to not contribute to Pryor or the other Democratic senators who voted against the background checks measure in April.

“When my dear innocent friend was shot to death, I didn’t blame guns. I blamed a system that makes it so terribly easy for criminals or the dangerous mentally ill to buy guns,” Angela Bradford-Barnes, who worked with Gwatney, says in the ad. “That’s why I was so disappointed when Mark Pryor voted against comprehensive background checks. On that vote, he let us down.”

Robert McLarty, a Democratic consultant in Little Rock who’s not affiliated with Pryor’s campaign, said the senator’s biggest challenge right now is that he doesn’t have an announced opponent while he’s fending off attacks from both sides.

“He’s not able to direct a compare and contrast style campaign,” McLarty said. “He’s not able to take a candidate on the other side and say this is how we differ.”

But McLarty and others say Pryor is in a better position than Lincoln was in 2010.

She survived a bruising Democratic primary with the help of former President Bill Clinton, who campaigned for her. But she lost handily in the fall of 2010. Pryor has higher approval figures than Lincoln did and appears unlikely at this point to draw a serious primary challenger next spring.

Clinton headlined a March fundraiser to kick off Pryor’s re-election bid, helping him raise more than $1 million in a night. Pryor reported having more than $3.4 million in the bank for the 2014 race.

“The reason this is a race of national significance is because it’s about whether a senator who cares about his own people more than ideological purity can be financed, elected, lifted by the people he has served in the face of all these crazy currents that are taking America and tearing it to shreds,” Clinton said at the event.

Pryor is trying to find middle ground on issues such as gun control, where he contends his vote represents a constituency that values hunting and gun rights. He’s also argued that a competing measure he supported that was endorsed by the National Rifle Association would have done more to address gun violence.

The NRA has also stepped in to help Pryor, with a radio ad airing in the state thanking the lawmaker for his vote.

Without an opponent, Pryor is casting the fight over gun control as one with Bloomberg.

“The mayor of New York City is running ads against me because I opposed President Obama’s gun control legislation. Nothing in the Obama plan would have prevented tragedies like Newtown, Aurora, Tucson or even Jonesboro,” Pryor says in his television ad. “I’m committed to finding real solutions to gun violence while protecting our Second Amendment rights.”

When Bloomberg’s group ran ads before the background checks vote, Pryor responded: “I don’t take gun advice from the mayor of New York City. I listen to Arkansans.”

He’s also distanced himself from Obama and national Democrats on other issues. He’s opposed gay marriage despite a growing chorus of support from lawmakers from his party in other states and criticized the Internal Revenue Service for targeting conservative groups.

Pryor said he’s trying to keep his focus on Arkansas.

“All I can do is be the very best senator I can be. I wish these outside groups would let me do that and not have to fool around with the election,” Pryor said. “People in Arkansas are tired of the election. They want us to get up to Washington and take care of the nation’s business.”